Can blender make online games
Depends on what you mean with "realtime blender online games".

Blender

Blender is a model editor and not sufficient to act as a game frame work.

BGE

The BGE is a full fledged game engine and can be used to create "realtime games". 

There is no build-in network support. You can communicate over a network via Python. This means you have to implement it by yourself (strong Python and network skills required).

Other Game Engines

You can use Blender to create assets to serve a game running on other game engines. It is up to this other engines to provide network support.